border-1px($color)
  position:relative
  &:after
    display:block
    position:absolute
    left:0
    bottom:0
    width:100%
    border-top:1px solid $color
    content:' '
//定义边框样式
// .border-1px
//    border-1px(rgba(7,17,27,0.1))

bg-image($url)
  background-image: url($url + "@2x.png")
  @media (-webkit-min-device-pixel-ratio: 3),(min-device-pixel-ratio: 3)
    background-image: url($url + "@3x.png")



